Spatial patterns in soil biogeochemical process rates along a Louisiana wetland salinity gradient in the Barataria Bay estuarine system

Tuesday, 16 December 2014
Brian J Roberts1, Matthew W Rich1, Hillary L Sullivan1, Regina Bledsoe2, Mia Dawson3, Brian Donnelly4 and John M Marton5, (1)Louisiana Universities Marine Consortium, Chauvin, LA, United States, (2)Nicholls State University, Thibodaux, LA, United States, (3)Oberlin College, Oberlin, OH, United States, (4)Villanova University, Villanova, PA, United States, (5)Indiana University Bloomington, Bloomington, IN, United States
Louisiana has the highest rates of coastal wetland loss in the United States. In addition to being lost, Louisiana wetlands experience numerous other environmental stressors including changes in salinity regime (both increases from salt water intrusion and decreases from the creation of river diversions) and climate change induced changes in vegetation (e.g. the northward expansion of Avicennia germinans (black mangrove) into salt marshes). In this study, we examined how these changes might influence biogeochemical process rates important in regulating carbon balance and the cycling, retention, and removal of nutrients in Louisiana wetlands. Specifically, we measured net soil greenhouse gas fluxes and collected cores for the determination of rates of greenhouse gas production, denitrification potential, nitrification potential, iron reduction, and phosphorus sorption from surface (0-5cm) and subsurface (10-15cm) depths for three plots in each of 4 sites along the salinity gradient: a freshwater marsh site, a brackish (7 ppt) marsh site, a salt marsh (17 ppt), and a Avicennia germinans stand (17 ppt; adjacent to salt marsh site) in the Barataria Bay estuarine system. Most biogeochemical processes displayed similar spatial patterns with salt marsh rates being lower than rates in freshwater and/or brackish marsh sites and not having significantly different rates than in Avicennia germinans stands. Rates in surface soils were generally higher than in subsurface soils. These patterns were generally consistent with spatial patterns in soil properties with soil water content, organic matter quantity and quality, and extractable nutrients generally being higher in freshwater and brackish marsh sites than salt marsh and Avicennia germinans sites, especially in surface soils. These spatial patterns suggest that the ability of coastal wetlands to retain and remove nutrients might change significantly in response to future climate changes in the region and that these alterations to biogeochemical cycling capacity need to be considering when designing and managing future restoration projects especially those involving river diversions.